1. Field of the Invention
The present invention relates to a drilling head with a cone rock bit.
2. Discussion of the Background
A rock bit of this kind is generally fitted with three cones and is in fact known by the name of a three-cone bit and is intended to be used, in particular, for deep boreholes, for example going down 3000 to 4000 meters or even more.
The drilling head has to operate under arduous conditions, that is to say in the presence of an abrasive drilling sludge and strong vibration, at a pressure often in excess of 400 bar (for the aforementioned depths) and at temperatures which may exceed 150xc2x0 C.
One of the crucial aspects of the rotary cones is their dynamic seal which has to remain effective under the aforementioned conditions.
There are currently two types of seals in existence which are used in the envisaged application, namely toric seals and metal-metal seals.
Drilling heads employing one or more toric seals are described, in particular, in American Patents U.S. Pat. No. 4,623,028 (Reed Tool Company), U.S. Pat. No. 5,456,327 (Smith International) and U.S. Pat. No. 5,129,471 (Hughes Tool Company).
Seals of the metal-to-metal type generally exhibit better life than toric seals. Seals of this type are described, for example in European Patent Application EP 138 737 (Hughes Tool), in American Patents U.S. Pat. No. 4,344,629, U.S. Pat. No. 4,824,123 and U.S. Pat. No. 4,822,057, all three of these being in the name of Smith International Inc., U.S. Pat. No.4,838,365 (Reed Tool Company) and U.S. Pat. No. 4,306,727 (Reed Rock Bit Company).
The problems posed by the design of this kind of seal have been set out in the article by Mike Hooper and Mark Hommel which was published in the minutes of the ASME Winter Annual Meeting, Dec. 1-6, 1991, Atlanta-Ga., under the reference 91-WA-DE-11 (p. 1-11) of The American Society of Mechanical Engineers (345 E. 47 St. New-York N.Y. 10017).
The subject of the present invention is a drilling head with a cone rock bit, in which a cone is sealed by a device which may be made of elastomer and which affords better performance by comparison with the toric seals.
Another object of the present invention is for sealing to be provided by a device which has a long life.
Another object of the invention is to allow the moving part to have an amplitude of deformation or even angular dislocation without the sealing being affected.
Another object of the present invention is for the sealing to be accompanied by effective consideration given to the back pressure generated by a pressure-compensating system.
Another object of the present invention is for the sealing to be easily fit into the cone.
At least one of the aforementioned objects is achieved, according to the present invention, by a drilling head with a cone rock bit. Each cone has a stationary part and a part which rotates about an axis of rotation. Also included is a dynamic sealing device between the stationary part and the rotary part, which is intended to avoid the ingress of drilling matter. The stationary part includes a pressure-compensating system capable at its output of delivering a product for lubricating the seal at a desired back pressure. Further, the sealing device is borne by the rotary part and has a first sealing lip and a second sealing lip, each of which forms a surface of revolution about the axis of rotation.
In addition, the first and second lips bear respectively against a first bearing face and a second bearing face secured to the stationary part. The first bearing face includes, for example, a track defmed by an annulus, the axis of which is the axis of rotation of the cone, and the second bearing face includes, for example, a track defined by a cylinder, the axis of which is the axis of rotation of the cone. The first sealing lip also has an outer face facing toward the drilling matter and an inner face facing toward a cavity which forms a reservoir of lubricating product. The second sealing lip has an outer face facing toward the outlet of the pressure-compensating system and an inner face facing toward said cavity. Further, the first lip is oriented in such a way that it presses against the first bearing face under the action of the pressure, and the second lip is oriented in such a w)ay that it moves away from the second bearing face under the action of the back pressure of the lubricating product. This allows the product to fill the cavity and compensate for the pressure in the cavity, particularly between the outer and inner faces of the first lip.
The first and/or the second sealing lip are advantageously made of elastomer. The second lip may have an annular bulge with a double chamfer forming a sharp edge which makes the seal.
At least one lip advantageously has a backing spring, for example a spring with prestressed turns constituting a toric annulus.
According to a preferred embodiment, the first lip and the second lip are borne by a first armature that revolves about the axis of rotation and which is secured to the rotary part. Further, at least one of the first and second lips has an extension which forms a static seal between the first armature and a wall of the rotary part. The first armature may consist of a single piece or alternatively may be made up of at least two parts joined together.
According to a particularly advantageous embodiment, the first bearing face and the second bearing face form part of a second armature consisting of a part that revolves about the axis of rotation and which is secured to the rotary part. Further, the second armature has a seal which makes a static seal between it and the rotary part.
The drilling head may also have a third sealing lip with an outer face facing toward said drilling matter and an inner face facing toward the outer face of the first sealing lip. dr
Other features and advantages of the invention will become more apparent from reading the description which will follow, which is given by way of nonlimiting example in conjunction with the drawings in which:
FIG. 1a depicts a part section of a rotary cone equipped with a seal according to the invention;
FIG. 1b depicts an enlarged detail of the seal according to FIG. 1a; 
FIG. 2 depicts an alternative form of the seal according to the invention;
FIG. 3 depicts a preferred embodiment of the invention and allowing the angular displacement of the tool to be decoded.